Interesterification can be either chemically or enzyme catalysed. If the interesterification is chemically catalysed, the fatty acids groups are rearranged randomly along the 3 positions of the glycerol backbone according to the law of probability. If the interesterification is enzyme catalysed, selectivity in the rearrangement of the fatty acids groups along the 3 positions of the glycerol backbone can be achieved.
Enzyme-catalysed interesterification is preferred over chemically-catalysed interesterification to reduce the amount of waste effluent and to reduce the use of chemicals.
However, the drawback of the enzyme catalysed interesterification is the relatively low activity and low stability of the enzymes used as catalyst. Indeed, enzymes show optimal activity when a precise set of conditions are met. In particular it is important to operate within a relatively narrow range of temperature, moisture content and in absence of impurities such as for example peroxides, aldehydes or ketones (resulting from the oxidation of oils and fats), phospholipids or soaps. When one or more of these conditions are not met, a denaturation or inactivation of the enzyme can take place, inducing a modification of its structure and hence a decrease or total loss of its activity. This denaturation is the mechanism behind the progressive loss of activity of the enzyme catalyst during the interesterification of fatty materials. A progressive loss of activity of the enzyme is observed even if highly refined fatty material is the feedstock of enzyme-catalysed interesterification. In fact, very minute amounts of impurities in the fatty material to be interesterified may lead to the progressive denaturation and loss of activity of the enzyme selected as catalyst. Therefore several methods have been proposed to purify and treat further fatty material used as feedstock of enzyme-catalysed interesterification, even if these fatty materials have already been previously purified by conventional processes in the oils and fats industry.
Examples of methods for purifying and further treating fatty material used as feedstock of enzyme-catalysed interesterification are disclosed U.S. Pat. No. 4,416,991A, in U.S. Pat. No. 4,861,716A, US 2005/0014237A1, US 2008/0057552A1 and WO 2008/069804A1.
U.S. Pat. No. 4,416,991A discloses a method for the enzymatic transesterification of a lipid which comprises continuously or repeatedly contacting an enzyme or an enzyme preparation having transesterification activities with a fresh supply of a dried fatty ester substrate while maintaining the total amount of water in the reaction system at or below the solubility limit of water in the fatty acid ester used.
U.S. Pat. No. 4,861,716A discloses a continuous interesterification process comprising the steps of: (a) precipitating a 1,3-specific lipase on inert particulate support material; (b) activating the lipase by addition of water in an amount effective to activate the lipase; (c) packing the inert support material carrying the precipitated lipase in a fixed bed; (d) preparing a fatty reactant mixture selected from the group consisting of fatty acids containing 3 to 20 carbon atoms, their esters including triglyceride oils and fats, their fractionated and hydrogenated derivatives, and combinations thereof; (e) dissolving water in said mixture in an amount sufficient to favor interesterification and minimize hydrolysis; (f) continuously flowing said mixture of step (e) through the fixed bed whereby a total contact time of less than two hours is achieved and glycerides in the 1,3-positions are formed; and (g) recovering from the solution of step (f), the glycerides enriched in the 1,3-positions.
JP 02-203789 A discloses that when oils and fats consisting of vegetable oil and/or animal oil are brought into contact with an immobilized enzyme obtained by absorbing and retaining a lipase onto a carrier and subjected to ester interchange reaction to modify oil and fats, an alkaline substance is added to the reaction system. The pH of the reaction liquid is preferably adjusted to by adding the alkaline substance to the reaction system. The carrier in which the lipase is absorbed and retained preferably includes a weakly acidic cation exchange resin. US 2008/0027552A1 reports that JP 02-203789A describes extending the half life of immobilized lipase by pre-treatment of the substrate with an alkaline substance. When an equal mixture of rapeseed oil and palm olein was interesterified on a column of lipase immobilized on Celite 535, the half life of the lipase was 18 hours. When the substrate was mixed with a solution of 1.8M potassium hydroxide (5 mL/kg substrate) the half life of the enzyme activity was 96 h.
JP 02-203790A discloses that when oils and fats consisting of vegetable oil and/or animal oil are brought into contact with an immobilized enzyme obtained by absorbing and retaining a lipase in a carrier and subjected to ester interchange reaction to modify oil and fats, a porous material is added to the reaction system. As the porous material, a material by which pH is turned to when the porous material is brought into contact with water is preferably used. The porous material includes e.g. a material obtained by treating molecular sieve, active carbon, diatomaceous earth or ion exchange resin with an alkaline aqueous solution. US 2008/0057552A1 reports that JP 02-203790A describes treating celite with sodium hydroxide and mixing this into the same substrate mixture. Using this approach, lipase half life was extended to 33 hours.
US 2005/0014237A1 discloses a method of making an esterified, transesterified or interesterified product comprising: (a) forming an initial substrate comprising one or more fats or oils; (b) deodorizing said initial substrate thereby reducing the constituents which cause or arise from fat or oil degradation in said initial substrate and thereby producing a deodorized substrate; (c) contacting said deodorized substrate with an enzyme thereby making said esterified, transesterified or interesterified product; wherein the half-life of said enzyme is prolonged.
US 2008/0057552A1 discloses a process for producing fats or oils comprising: placing a glyceride in contact with a compound selected from the group consisting of granular clay, granular carbon, and a combination thereof, thus forming a purified substrate; and placing the purified substrate in contact with a lipase, thus producing the fat or the oil.
WO 2008/069804A1 discloses a method for continuous enzymatic treatment of a lipid-containing composition at a substantially constant flow rate, the method comprising the steps of (a) providing a lipid-containing feedstock, (b) contacting said feedstock with a first processing aid to pre-treat the feedstock, (c) causing said feedstock to pass at a substantially constant flow rate through a treatment system comprising a plurality of enzyme-containing fixed bed reactors connected to one another in series, and (d) said fixed bed reactors being individually serviceable, the flow rate of the feedstock remaining substantially constant through the treatment system when one of said fixed bed reactors is taken off-line for servicing with preferred processing aids including chromatographic silica, fused silica, precipitated silica, fumed silica, colloidal silica, amorphous silica, silica hydrogel, and sodium aluminium silicate.
While the prior art methods described here above are indeed directed to increase the activity and/or the life-time of the enzyme by either removing impurities contained in the fatty material and/or either adjusting favourably the fatty material moisture content or acidity, those methods include various drawbacks. Use of packed column(s) loaded with, for example, chromatographic grade silica or clays will induce a pressure increase caused by the progressive fouling of the adsorbent material. Additionally, such adsorbents may release unknown contaminants that may be complicated to remove and even affect enzyme activity negatively. Addition of a relatively large amount of aqueous potassium hydroxide (5 mL/kg substrate) to the fatty material will induce extensive hydrolysis leading to unacceptable amount of free fatty acids and partial glycerides. Instant deodorisation performed just before the interesterification process will require high capital investment before being put into practice and hence will result in higher processing costs.
An often underestimated issue is that the enzyme carrier can release minor components that may have negative effect on oil quality requiring thus additional post-purification. For example release of off-flavours has been observed in several instances.
Accordingly, there remains a need in the art to overcome the limitation of the existing pre-treatment processes of fatty materials intended for the enzymatic catalysed interesterification.